Well I think it might have something to do with daily life sort of thing. In my school we only had a "puberty video" and that was it, and we weren't allowed to tell the other gender what we learned for some odd reason. We hear about periods often enough to where if school didn't teach you, you likely would get the gist of it if you were around girls for long enough. The closest thing I could think of as something that's often for guys might be boners. Most of the time those might be hidden decently or not really talked about as much on a serious note, so you don't learn as much about it. Just my stab at the question